1. Field of the Invention
Embodiments of the invention relate to methods for making nano-whiskers and films comprising nano-whiskers and more particularly to tin oxide films comprising nano-whiskers.
2. Technical Background
Nanowire structures have shown advantages in gas sensing, and in optical and electronic applications. Conventional methods of making nanowire structures include chemical vapor deposition (CVD), atmospheric pressure chemical vapor deposition (APCVD), physical vapor deposition (PVD), sol-gel, hydrothermal and electrochemical deposition methods. These methods can be advantageous in large scale nanowire production or making ordered or aligned nanowire structures.
Transparent and/or electrically conductive film coated glass is useful for a number of applications, for example, in display applications such as the back plane architecture of display devices, for example, liquid crystal displays (LCD), and organic light-emitting diodes (OLED) for cell phones.
Transparent conductive oxides (TCO) are widely used in LCD display panels, Low-E windows, E-papers, and in many other industrial applications. Though, cadmium oxide (CdO) is historically the first TCO discovered around 1907, today the most used TCOs are indium tin oxide (ITO) and fluorine doped tin oxide (FTO) found in the various display panels and the low-E windows, respectively.
TCOs are wide-band semiconductors in nature (hence the visible transmission and conductivity); and are mostly n-type with Fermi-level, ΔE˜kT, right below the conduction band minimum. The first useful p-type TCO (i.e., CuAlO2) was realized later in 1997 and the field of next-generation “transparent electronics” has since emerged. However, there is a need for high performing TCOs as transparent electrodes in thin film PV technology that has drawn much of the attention lately.
In this regard, one of the most recent developments is in thin-film silicon tandem PV cells, which calls for an application-specific TCO with light trapping capability for improved solar-light absorption in the micro-crystalline silicon layer in order to increase cell efficiency. Commercially available textured FTO on soda-lime glass is an example of an FTO currently used in PV cells.
Typically, deposition of transparent conductive films on glass substrates is performed in a vacuum chamber either by sputtering or by chemical vapor deposition (CVD), for example, plasma enhanced chemical vapor deposition (PECVD), spray coating, or metal vapor deposition followed by oxidation. With the exception of spray coating, these coating processes are high cost processes. They either typically operate in vacuum or use expensive precursors. Spray coating is cost effective, but usually results in nonuniform coating with defect sites on the coated films.
Sputtering of transparent conductive films on glass, for example, sputter deposition of indium doped tin oxide on glasses, has one or more of the following disadvantages: large area sputtering is challenging, time consuming, and generally produces non-uniform films on glass substrates, especially glass substrates of increased size, for example, display glass for televisions.
The glass cleaning prior to coating in several conventional coating methods introduces complexity and additional cost. Also, several conventional coating methods require a doping of the coating which is typically difficult and introduces additional processing steps.
It would be advantageous to develop a method for coating a glass substrate with a tin-oxide film which has a texture. It would also be advantageous for the tin-oxide film to be conductive and be useful for TCO applications.